Variable displacement engines (VDE) can operate in a partial-cylinder operation mode to reduce fuel usage. However, such a partial-cylinder operation may increase noise, vibration and harshness (NVH) compared to an all-cylinder operation, and the increased NVH may degrade drive feel and/or driver comfort.
Torque converters which can provide a fluid coupling between the engine and the transmission may be operated in an unlocked or partially unlocked state to absorb torque fluctuation and improve NVH. However fuel efficiency may be compromised as a result, since a portion of engine torque energy (in general up to 10%) may be lost as a result of the torque converter fluid coupling. To control the amount of torque converter fluid coupling and therefore the torque energy loss, slip control clutches may be added to a torque converter, and the amount of fluid coupling is controlled by controlling the slip rotation rate or slip of the torque converter. The more slip is allowed by the slip control clutch, the more fluid the coupling between the engine and the transmission, the more torque fluctuation is absorbed, which translates to better NVH, but in the mean time more engine torque energy will also be lost; and vice versa. A trade-off therefore exists between fuel economy and NVH in adjusting the torque converter slip rotation rate. Similarly, trade-offs between fuel economy and NVH may also exist for adjusting other vehicular parameters.
The inventors herein have recognized that various drivers under different drive conditions may wish to make different tradeoffs between fuel economy and NVH. For example, one driver may prefer improved fuel economy while another may prefer an improved NVH, or the same driver may prefer improved fuel economy in one instance but may prefer an improved NVH in another.
The inventors recognize that the above issues may be addressed by providing a driver interface that allows a driver to select a drive mode or preference setting that reflects the driver's preference over fuel economy and NVH trade-off. Vehicle operating parameters may then be adjusted according to the driver selected drive mode. For example, the slip rotation rate or slip profile of a slip control clutch may be adjusted to reflect the driver selected preference setting or tradeoff between fuel economy and NVH in a variable displacement engine, as well as the cylinder deactivation state.